arcab4,
i also keep discus, i would probably say that a good temperature range for them is between 82F and 86F. you are right that some plants cannot handle that temperature but there are some that will thrive in that temperature. The vals should do fine, but i have never tried glosso, but you could try some swords, crypts, anubias, java moss, java fern, etc. there are many plants that can work up in that temperature range. hope all works out all right. ;D
Joe - aka discusaquarium